The present inventions relates to a filter life sensor. In particular, the present invention relates to a dielectric filter life sensor.
Air handling systems, such as air furnaces, air conditioning systems, and room air purifiers, typically include filters to take the dust and other particulate matter out of the air. When these filters become dirty, the air flow through the filter is reduced. The filters therefore must be periodically changed or cleaned to maintain the efficiency of the air handling system. A typical recommendation is to change a filter on a household air handling system every three months. It is often difficult for users to remember to change the filter. Additionally, a recommendation for changing a filter based on a predetermined time does not factor in the actual conditions of the environment. In some instances, the filter may become clogged before the suggested three months, and in some conditions the filter may still adequately perform beyond three months.
Filter change sensor systems exist for measuring the end of the useful life of a filter. Such systems may include a device, such as a float, for measuring the pressure drop across the filter. These systems are generally complicated and some require sensor placement on each side of the filter for measuring the pressure drop. Some of these systems measure the air velocity through the filter. However, because the area of filters is generally large, the air velocity through a filter is quite low and measuring the actual quantity of air passing through the filter is difficult. In such cases, sensitive, specialized equipment is necessary to obtain accurate readings, which are expensive and not practical for consumer use.
Other systems exist that include an air bypass through or around the filter. In such systems, when the filter collects dirt and dust, the overall air flow is restricted causing more air to flow through the bypass, which in some cases is a whistle device. These systems will then whistle when the air flow through the bypass reaches a threshold level. These systems do not give a read-out, either a digital or analog signal, on the level of filter use. Additionally, these systems only indicate filter performance at the filter location and therefore do not communicate with the thermostat, which is normally placed at the location more visible to the user. Therefore, it would be desirable to have a low-cost filter sensor that is able to determine the actual end of the useful life of the filter.